Title: How do arboviruses escape the mosquito midgut? - Analysis of a novel mechanism Project Summary. Following ingestion of a viremic bloodmeal from a vertebrate host, an arbovirus enters the midgut lumen of a mosquito vector (such as Aedes aegypti) along with the bloodmeal. The virus then needs to enter and infect the midgut epithelial cells of the midgut before the virus disseminates from the midgut to secondary tissues including the salivary glands. Once these are infected, the mosquito transmits the virus to another vertebrate host during probing. The molecular nature of the exit mechanism of the virus from the midgut, has been unresolved so far. In this grant application, we will reveal this mechanism and its genetic background using a multifaceted portfolio of state-of-the-art methodologies. Our previous studies demonstrated that during bloodmeal digestion, chikungunya virus (CHIKV) exits the mosquito midgut via the basal lamina (BL) surrounding the organ. The BL predominantly consists of collagen IV and laminin and its typical pore size exclusion limit appears to be too small for virions to pass through. However, during bloodmeal digestion, the BL alters its structure as midgut-associated collagen IV becomes greatly diminished. We hypothesized that it is this structural change in the BL that allows virions to exit the midgut during bloodmeal digestion. In eukaryotes, known proteinases that modify the extracellular matrix including the BL are matrix metalloproteinases, ADAM/ADAMTS, and serine collagenases. We hypothesize that these classes of proteinases, which are also present in mosquitoes, are responsible for midgut BL modification during bloodmeal digestion. To test these two hypotheses, we propose the following three Specific Aims for this application: 1.) Analyze BL degradation/remodeling and CHIKV dissemination in Ae. aegypti by ultrastructural studies and proteomic analysis; 2.) Identify proteinases that are involved in the BL modification process during bloodmeal digestion and CHIKV dissemination; 3.) Assess whether other viruses (such as Zika, dengue, and Mayaro viruses) utilize the same midgut escape mechanism as observed for CHIKV and how transgenic manipulation of proteinase-of-interest expression affects viral midgut escape in mosquitoes. Completion of these Specific Aims will provide a comprehensive picture explaining the mechanism of the midgut escape barrier, which key enzymes are involved in the mechanism, and whether the mechanism elucidated for CHIKV is the paradigm for other arboviruses. Our results will be critical for developing novel control strategies aimed at manipulating arbovirus midgut escape in mosquitoes. Our findings will also provide the research community with the possibility to develop novel genetic markers for vector competence based on midgut escape.